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Fuel Gauges Over-reading

D

DaveHadfield

Member
Hi, we could use some input...

We have a 1999 RV6A. We didn't build it.

I don't trust fuel gauges, so calibrated a dipstick when we first started to fly it. This works perfectly. But my wife flies this aircraft more than I do, and she'd like fuel gauges that work.

Right now, when the gauges say 1/4, the tank has a measured 1 US Gal left. (Proven after landing by the dipstick.) Both are the same. We know about the fact that the gauges don't start to work until the fuel drops to about 15 US Gal or so, and can live with that.

Questions:

1) Is this aircraft likely to have the float-type sensors, or the capacitance? And, how do you tell?
2) Is there a likely fix for this? Might it be a grounding issue? I'm afraid I'm a lot better with structures than electronics. I don't know anything about how this system is grounded.

Thanks in advance,

Dave
 
I'll tell you what I did. I'd circle over an airport you know very well at say 10000 Ft. Be low on fuel when you do it. Run one tank dry and watch your fuel gauge closely as you're doing it. If the needle hits empty before the engine starts to run out of gas, time it on your watch. Maybe its the other way and it starts to quit while the gauge still shows fuel. Either way, now you know. Switch to your good tank and land normally. Then do the same procedure the other way around for your other tank.

Oh, and I might add, try as much as possible not to be in any bank while you're doing this.

Cheers
 
Last edited:
Gauge calibration

Dave,
I recently asked if any electrical types knew how to "electrically trim" the Vans float gauges to be accurate at your measured " minimum fuel level" you want to be aware of. I got a good answer regarding adding resistance in series to adjust the reading. You should be able to find the threads under my name.
 
If they ere the vans round gauges they are most likely floats. They can be adjusted by bending the float arm. Big downside is you have to pull the senders out of the wing roots to do it.
 
The "reading full until not nearly full" issue is present with all of the float senders. The float is at the inboard end of the tank, and, because of dihedral, you have to use a substantial amount of fuel before the fuel level begins to drop at the root end. Basically, you're stuck with that issue.

On the low end of the scale, you should be able to pull the sender and reshape the float arm to give you more accurate readings.
 
There was a big discussion recently about measuring fuel consumption. I don't rely on my fuel gauges entirely, but they are VERY accurate. They are probably a Vans part but are marked in gallons not 1/4's. I've tested them several times down to 2.5 gallons and they have always been spot on. So I am saying you can do better than you have now. But I also time my tanks, and I have a fuel totalizer. Like was discussed in the other thread. I feel better when everything agrees, and I can always verify this with how much fuel I put back in later.

But again, if you are bending the float lever in a trial and error fashion, maybe look at some other senders. I remember my builder telling me they were calibrated at 2.5 gallons. I never (yet...) fly them lower than 5 gallons in practice.
 
An easy way is to drain the tanks, level the plane and put 2 gals at a time into the tanks and mark the Ga. This should be good up to about 14-15 Gal. due to the dihedral of the wing. Of course this assuming that it is a mechanical Ga. Electronic gauges have their own instruction on how to calibrate.

To check usable fuel, while the tank is empty turn on the boost pump, add fuel until the pump picks up fuel, you will hear it as the pump changes noise. If it takes more than a quart of fuel You might suspect a problem with the pick up. Unusable fuel in an RV is usually a fairly small amount.

Larry
 
Thanks for the replies!

I am NOT pulling the fuel tanks out.

We did a complete empty of the tank, then put in a measured 2 gal at a time, marking a stick as we did so. Thus we have a graduated dipstick that is perfect for our airplane.

The panel gauge shows 1/4 when the tank has only 1 gal in it -- that's the problem. Obviously it's dangerous.

Larry DeCamp, that's sounds perfect. I'll research.

Much obliged,

Dave
 
Dave, I have solved this problem by a combination of resistors. Just start with a 10 ohm resistor "from Radio Shack" in line with the sender wire. This will drop the needle about 1/16th of 1 inch. Then start to parallel the same value one at a time until the needle falls to the stop. Your end value will probably be in the area of 1 to 2 ohms. It works perfect on the low side which is where you need it. Then measure the value of the parallel resistors and you can order the exact value you need. Five 10 ohm resistors in parallel equal 2 ohms and that is what fixed mine.
 
I would recommend putting in a digital fuel level display that can be calibrated. Though Van's gauges may be better than typical certified needle gauges, I have never seen a needle gauge anywhere close to as accurate as a digital gauge. I just fueled my -6A today. The amount that the floats said I had were within a gallon of my totalizer, which was almost exactly what it took to fill it up.
 
DaveHadfield said:
Thanks for the replies!

I am NOT pulling the fuel tanks out.

We did a complete empty of the tank, then put in a measured 2 gal at a time, marking a stick as we did so. Thus we have a graduated dipstick that is perfect for our airplane.

The panel gauge shows 1/4 when the tank has only 1 gal in it -- that's the problem. Obviously it's dangerous.

Larry DeCamp, that's sounds perfect. I'll research.

Much obliged,

Dave
Click to expand...

You don't need to pull the tank to pull and adjust the arm on the fuel sender. There is (barely) enough access in the wing root.
 
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